Iron-sulfur proteins in oriented submitochondrial particles will be studied using EPR at low temperatures to determine protein orientation relative to the mitochondrial membrane. Magnetic interactions between centers will also be studied by investigating line broadening and splitting, relaxation phenomena, and half-field signals. Computer simulation programs will be developed to assist in the analysis of the data. The resulting information will enable us to specify the relative positions (distance and direction) of interacting centers with the oriented membrane multilayer.